'\" t
.TH "SD_BUS_MESSAGE_APPEND_ARRAY" "3" "" "systemd 256.7" "sd_bus_message_append_array"
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.SH "NAME"
sd_bus_message_append_array, sd_bus_message_append_array_memfd, sd_bus_message_append_array_iovec, sd_bus_message_append_array_space \- Append an array of fields to a D\-Bus message
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <systemd/sd\-bus\&.h>
.fi
.ft
.HP \w'int\ sd_bus_message_append_array('u
.BI "int sd_bus_message_append_array(sd_bus_message\ *" "m" ", char\ " "type" ", const\ void\ *" "ptr" ", size_t\ " "size" ");"
.HP \w'int\ sd_bus_message_append_array_memfd('u
.BI "int sd_bus_message_append_array_memfd(sd_bus_message\ *" "m" ", char\ " "type" ", int\ " "memfd" ", uint64_t\ " "offset" ", uint64_t\ " "size" ");"
.HP \w'int\ sd_bus_message_append_array_iovec('u
.BI "int sd_bus_message_append_array_iovec(sd_bus_message\ *" "m" ", char\ " "type" ", const\ struct\ iovec\ *" "iov" ", unsigned\ " "n" ");"
.HP \w'int\ sd_bus_message_append_array_space('u
.BI "int sd_bus_message_append_array_space(sd_bus_message\ *" "m" ", char\ " "type" ", size_t\ " "size" ", void\ **" "ptr" ");"
.SH "DESCRIPTION"
.PP
The
\fBsd_bus_message_append_array()\fR
function appends an array to a D\-Bus message
\fIm\fR\&. A container will be opened, the array contents appended, and the container closed\&. The parameter
\fItype\fR
determines how the pointer
\fIp\fR
is interpreted\&.
\fItype\fR
must be one of the "trivial" types
"y",
"n",
"q",
"i",
"u",
"x",
"t",
"d"
(but not
"b"), as defined by the
\m[blue]\fBBasic D\-Bus Types\fR\m[]\&\s-2\u[1]\d\s+2
section of the D\-Bus specification, and listed in
\fBsd_bus_message_append_basic\fR(3)\&. Pointer
\fIp\fR
must point to an array of size
\fIsize\fR
bytes containing items of the respective type\&. Size
\fIsize\fR
must be a multiple of the size of the type
\fItype\fR\&. As a special case,
\fIp\fR
may be
\fBNULL\fR, if
\fIsize\fR
is 0\&. The memory pointed to by
\fIp\fR
is copied into the memory area containing the message and stays in possession of the caller\&. The caller may hence freely change the data after this call without affecting the message the array was appended to\&.
.PP
The
\fBsd_bus_message_append_array_memfd()\fR
function appends an array of a trivial type to message
\fIm\fR, similar to
\fBsd_bus_message_append_array()\fR\&. The contents of the memory file descriptor
\fImemfd\fR
starting at the specified offset and of the specified size is used as the contents of the array\&. The offset and size must be a multiple of the size of the type
\fItype\fR\&. However, as a special exception, if the offset is specified as zero and the size specified as UINT64_MAX the full memory file descriptor contents is used\&. The memory file descriptor is sealed by this call if it has not been sealed yet, and cannot be modified after this call\&. See
\fBmemfd_create\fR(2)
for details about memory file descriptors\&. Appending arrays with memory file descriptors enables efficient zero\-copy data transfer, as the memory file descriptor may be passed as\-is to the destination, without copying the memory in it to the destination process\&. Not all protocol transports support passing memory file descriptors between participants, in which case this call will automatically fall back to copying\&. Also, as memory file descriptor passing is inefficient for smaller amounts of data, copying might still be enforced even where memory file descriptor passing is supported\&.
.PP
The
\fBsd_bus_message_append_array_iovec()\fR
function appends an array of a trivial type to the message
\fIm\fR, similar to
\fBsd_bus_message_append_array()\fR\&. Contents of the I/O vector array
\fIiov\fR
are used as the contents of the array\&. The total size of
\fIiov\fR
payload (the sum of
\fIiov_len\fR
fields) must be a multiple of the size of the type
\fItype\fR\&. The
\fIiov\fR
argument must point to
\fIn\fR
I/O vector structures\&. Each structure may have the
iov_base
field set, in which case the memory pointed to will be copied into the message, or unset (set to zero), in which case a block of zeros of length
iov_len
bytes will be inserted\&. The memory pointed at by
\fIiov\fR
may be changed after this call\&.
.PP
The
\fBsd_bus_message_append_array_space()\fR
function appends space for an array of a trivial type to message
\fIm\fR\&. It behaves the same as
\fBsd_bus_message_append_array()\fR, but instead of copying items to the message, it returns a pointer to the destination area to the caller in pointer
\fIp\fR\&. The caller should subsequently write the array contents to this memory\&. Modifications to the memory pointed to should only occur until the next operation on the bus message is invoked\&. Most importantly, the memory should not be altered anymore when another field has been added to the message or the message has been sealed\&.
.SH "RETURN VALUE"
.PP
On success, these calls return 0 or a positive integer\&. On failure, they return a negative errno\-style error code\&.
.SS "Errors"
.PP
Returned errors may indicate the following problems:
.PP
\fB\-EINVAL\fR
.RS 4
Specified parameter is invalid\&.
.RE
.PP
\fB\-EPERM\fR
.RS 4
Message has been sealed\&.
.RE
.PP
\fB\-ESTALE\fR
.RS 4
Message is in invalid state\&.
.RE
.PP
\fB\-ENXIO\fR
.RS 4
Message cannot be appended to\&.
.RE
.PP
\fB\-ENOMEM\fR
.RS 4
Memory allocation failed\&.
.RE
.SH "NOTES"
.PP
Functions described here are available as a shared library, which can be compiled against and linked to with the
\fBlibsystemd\fR\ \&\fBpkg-config\fR(1)
file\&.
.PP
The code described here uses
\fBgetenv\fR(3), which is declared to be not multi\-thread\-safe\&. This means that the code calling the functions described here must not call
\fBsetenv\fR(3)
from a parallel thread\&. It is recommended to only do calls to
\fBsetenv()\fR
from an early phase of the program when no other threads have been started\&.
.SH "SEE ALSO"
.PP
\fBsystemd\fR(1), \fBsd-bus\fR(3), \fBsd_bus_message_append\fR(3), \fBsd_bus_message_append_basic\fR(3), \fBmemfd_create\fR(2), \m[blue]\fBThe D\-Bus specification\fR\m[]\&\s-2\u[2]\d\s+2
.SH "NOTES"
.IP " 1." 4
Basic D-Bus Types
.RS 4
\%https://dbus.freedesktop.org/doc/dbus-specification.html#basic-types
.RE
.IP " 2." 4
The D-Bus specification
.RS 4
\%https://dbus.freedesktop.org/doc/dbus-specification.html
.RE
